Clothing made from cellulose fabrics such as cotton is well known. For example, a denim fabric has been used for many years to manufacture work clothes such as jeans. Such clothing was produced with a starch based sizing that eased the manufacturing and handling processes, but resulted in a stiff relatively uncomfortable garment. Also, the fabric had been dyed with a dark blue indigo that, when washed, bled from the fabric. Thus, after a substantial period of wear and washing, the denim fabric lightened in color and the garment became more pliable and comfortable. In addition, the fabric took on a used or distressed appearance, particularly on the seams, panels and raised areas where the stitching had been made.
In time, and particularly recently, denim clothing has become more popular. Denim fabrics are being utilized not only to make work clothes, but for jackets, coats, shirts and a seemingly endless variety of other garments. The used or distressed look has likewise become fashionable. As a result, manufacturers of denim clothing have developed methods by which to distress denim fabric. One method employed to distress a denim fabric is known as "acid washing." This method typically consists of abrading the denim fabric through the use of pumice stones or some other abrading device such as silica sand to produce a softer, more pliable fabric with random, localized areas of lighter color.
Described more particularly, acid washing of a denim garment has been accomplished by the following steps. A quantity of garments are first washed in a solution to remove the starch-based sizing. The garments are then dry tumbled in a quantity of pumice rock or silica sand that has been impregnated with an oxidizer solution, usually potassium permanganate. After tumbling, the garments are washed in a neutralizing solution to remove any excess oxidizer. The garments are then dried in a conventional manner.
Other methods of distressing denim or other fabrics are known. For example, U.S. Pat. No. 4,740,213, issued on Apr. 26, 1988 to Francesco Ricci, discloses a method of producing a random faded effect on cloth or made-up garments, and the endproduct obtained by implementation of such a method. The method described in this patent comprises the steps of bleaching the cloth in a dry state, utilizing granules of pumice or similar materials impregnated with a fluid having powerful bleaching properties, tumbling the granules and cloth together in a rotating drum such that close contact is brought about between the two, recovering the granules following rotation of the drum for a set duration, and neutralizing any residual bleaching agent held in the cloth by washing and drying.
Another method of distressing fabrics is disclosed in U.S. Pat. No. 4,850,156, issued on Jul. 25, 1989 to David L. Bellaire. This patent discloses a method of preparing porous abrasive rock for use in distressing fabric including the steps of impregnating rocks placed in a vacuum vessel with a bleaching solution under reduced pressure, maintaining the reduced pressure for a first interval while injecting the solution beneath the rocks, and then increasing the vessel pressure above ambient for a second interval prior to removal and use of the rocks to abrade fabric.
These method have provided a distressed appearance to the denim fabric suitable for the many types of denim garments. However, it has been observed that the acid-washed denim fabric is susceptible to yellowing when exposed to ultraviolet light, such as sunlight. Such latent yellowing of the fabric is undesirable. Further, the intensity of the yellowing increases with the duration of the fabric's exposure to ultraviolet light. In some instances, the yellowing can be so severe that the finished garment is rendered unsaleable. It is not unusual for otherwise acceptable denim garments to yellow sufficiently to render the garments unsaleable. Thus, manufacturers of acid washed or distressed denim clothing seek to inhibit, if not eliminate, yellowing of the denim fabric.
Yellowing of the denim fabric is believed to result from the presence of anthranilic acid on or in the garment. The anthranilic acid is believed to be produced during the acid washing process. As noted above, denim fabric is conventionally treated with the well-known dye indigo. While naturally available, indigo dye can be and is synthesized for industrial use. Synthesized indigo dye is usually a blue powdery material with a copper luster. The principal coloring matter of indigo dye has a chemical formula of C.sub.16 H.sub.10 O.sub.2 N.sub.2. During the acid washing process, the indigo dye oxidizes to produce isatin, a crystalline compound or indole that has oxygen molecules at carbon positions "2" and "3". Isatin is commonly orange to red in color, water soluble and has a chemical formula of C.sub.6 H.sub.5 NO.sub.1.
As also noted above, at least one method of preparing pumice stones for use in the acid washing process is to soak or otherwise impregnate the stones with a bleaching agent such as potassium permanganate, KM.sup.n O.sub.4. An excess amount of potassium permanganate is usually present in the acid wash process. It is believed that this excess of potassium permanganate facilitates further oxidation of the isatin, resulting in the formation of anthranilic acid. Anthranilic acid is a white to pale powder and water soluble. It is known that, in time, anthranilic acid discolors to a yellow color. The chemical reaction whereby the anthranilic acid becomes discolored is not known to the inventor. However, the inventor is aware of the fact that such discoloring occurs. It is believed by the inventor that the presence of anthranilic acid on or within the distressed denim material is a, if not the, primary cause of the latent yellowing which occurs when acid-washed denim garments are exposed to ultraviolet light.
There is a need in the art, therefore, for a composition and method by which to inhibit the yellowing of denim fabric. This need has been recognized previously. Various chemicals have been used to attempt to combat this problem including ultraviolet and ozone inhibitors. For example, different methods and chemicals have been used to try to neutralize the bleaching agent in an effort to inhibit yellowing. Some of these attempts have included treating the acid-washed denim fabric with bi-sulfates. These methods, however, are expensive and have met with limited success. The need for a cost effective method and composition for inhibiting the yellowing of distressed denim fabric thus remains.